from __future__ import annotations
import re
from typing import TYPE_CHECKING
import numpy as np
from pandas.util._decorators import Appender
from pandas.core.dtypes.common import is_list_like
from pandas.core.dtypes.concat import concat_compat
from pandas.core.dtypes.missing import notna
import pandas.core.algorithms as algos
from pandas.core.arrays import Categorical
import pandas.core.common as com
from pandas.core.indexes.api import (
Index,
MultiIndex,
)
from pandas.core.reshape.concat import concat
from pandas.core.reshape.util import tile_compat
from pandas.core.shared_docs import _shared_docs
from pandas.core.tools.numeric import to_numeric
if TYPE_CHECKING:
from collections.abc import Hashable
from pandas._typing import AnyArrayLike
from pandas import DataFrame
@Appender(_shared_docs["melt"] % {"caller": "pd.melt(df, ", "other": "DataFrame.melt"})
def melt(
frame: DataFrame,
id_vars=None,
value_vars=None,
var_name=None,
value_name: Hashable = "value",
col_level=None,
ignore_index: bool = True,
) -> DataFrame:
# If multiindex, gather names of columns on all level for checking presence
# of `id_vars` and `value_vars`
if isinstance(frame.columns, MultiIndex):
cols = [x for c in frame.columns for x in c]
else:
cols = list(frame.columns)
if value_name in frame.columns:
raise ValueError(
f"value_name ({value_name}) cannot match an element in "
"the DataFrame columns."
)
if id_vars is not None:
if not is_list_like(id_vars):
id_vars = [id_vars]
elif isinstance(frame.columns, MultiIndex) and not isinstance(id_vars, list):
raise ValueError(
"id_vars must be a list of tuples when columns are a MultiIndex"
)
else:
# Check that `id_vars` are in frame
id_vars = list(id_vars)
missing = Index(com.flatten(id_vars)).difference(cols)
if not missing.empty:
raise KeyError(
"The following 'id_vars' are not present "
f"in the DataFrame: {list(missing)}"
)
else:
id_vars = []
if value_vars is not None:
if not is_list_like(value_vars):
value_vars = [value_vars]
elif isinstance(frame.columns, MultiIndex) and not isinstance(value_vars, list):
raise ValueError(
"value_vars must be a list of tuples when columns are a MultiIndex"
)
else:
value_vars = list(value_vars)
# Check that `value_vars` are in frame
missing = Index(com.flatten(value_vars)).difference(cols)
if not missing.empty:
raise KeyError(
"The following 'value_vars' are not present in "
f"the DataFrame: {list(missing)}"
)
if col_level is not None:
idx = frame.columns.get_level_values(col_level).get_indexer(
id_vars + value_vars
)
else:
idx = algos.unique(frame.columns.get_indexer_for(id_vars + value_vars))
frame = frame.iloc[:, idx]
else:
frame = frame.copy()
if col_level is not None: # allow list or other?
# frame is a copy
frame.columns = frame.columns.get_level_values(col_level)
if var_name is None:
if isinstance(frame.columns, MultiIndex):
if len(frame.columns.names) == len(set(frame.columns.names)):
var_name = frame.columns.names
else:
var_name = [f"variable_{i}" for i in range(len(frame.columns.names))]
else:
var_name = [
frame.columns.name if frame.columns.name is not None else "variable"
]
if isinstance(var_name, str):
var_name = [var_name]
N, K = frame.shape
K -= len(id_vars)
mdata: dict[Hashable, AnyArrayLike] = {}
for col in id_vars:
id_data = frame.pop(col)
if not isinstance(id_data.dtype, np.dtype):
# i.e. ExtensionDtype
if K > 0:
mdata[col] = concat([id_data] * K, ignore_index=True)
else:
# We can't concat empty list. (GH 46044)
mdata[col] = type(id_data)([], name=id_data.name, dtype=id_data.dtype)
else:
mdata[col] = np.tile(id_data._values, K)
mcolumns = id_vars + var_name + [value_name]
if frame.shape[1] > 0:
mdata[value_name] = concat(
[frame.iloc[:, i] for i in range(frame.shape[1])]
).values
else:
mdata[value_name] = frame._values.ravel("F")
for i, col in enumerate(var_name):
mdata[col] = frame.columns._get_level_values(i).repeat(N)
result = frame._constructor(mdata, columns=mcolumns)
if not ignore_index:
result.index = tile_compat(frame.index, K)
return result
[docs]def lreshape(data: DataFrame, groups, dropna: bool = True) -> DataFrame:
"""
Reshape wide-format data to long. Generalized inverse of DataFrame.pivot.
Accepts a dictionary, ``groups``, in which each key is a new column name
and each value is a list of old column names that will be "melted" under
the new column name as part of the reshape.
Parameters
----------
data : DataFrame
The wide-format DataFrame.
groups : dict
{new_name : list_of_columns}.
dropna : bool, default True
Do not include columns whose entries are all NaN.
Returns
-------
DataFrame
Reshaped DataFrame.
See Also
--------
melt : Unpivot a DataFrame from wide to long format, optionally leaving
identifiers set.
pivot : Create a spreadsheet-style pivot table as a DataFrame.
DataFrame.pivot : Pivot without aggregation that can handle
non-numeric data.
DataFrame.pivot_table : Generalization of pivot that can handle
duplicate values for one index/column pair.
DataFrame.unstack : Pivot based on the index values instead of a
column.
wide_to_long : Wide panel to long format. Less flexible but more
user-friendly than melt.
Examples
--------
>>> data = pd.DataFrame({'hr1': [514, 573], 'hr2': [545, 526],
... 'team': ['Red Sox', 'Yankees'],
... 'year1': [2007, 2007], 'year2': [2008, 2008]})
>>> data
hr1 hr2 team year1 year2
0 514 545 Red Sox 2007 2008
1 573 526 Yankees 2007 2008
>>> pd.lreshape(data, {'year': ['year1', 'year2'], 'hr': ['hr1', 'hr2']})
team year hr
0 Red Sox 2007 514
1 Yankees 2007 573
2 Red Sox 2008 545
3 Yankees 2008 526
"""
if isinstance(groups, dict):
keys = list(groups.keys())
values = list(groups.values())
else:
keys, values = zip(*groups)
all_cols = list(set.union(*(set(x) for x in values)))
id_cols = list(data.columns.difference(all_cols))
K = len(values[0])
for seq in values:
if len(seq) != K:
raise ValueError("All column lists must be same length")
mdata = {}
pivot_cols = []
for target, names in zip(keys, values):
to_concat = [data[col]._values for col in names]
mdata[target] = concat_compat(to_concat)
pivot_cols.append(target)
for col in id_cols:
mdata[col] = np.tile(data[col]._values, K)
if dropna:
mask = np.ones(len(mdata[pivot_cols[0]]), dtype=bool)
for c in pivot_cols:
mask &= notna(mdata[c])
if not mask.all():
mdata = {k: v[mask] for k, v in mdata.items()}
return data._constructor(mdata, columns=id_cols + pivot_cols)
[docs]def wide_to_long(
df: DataFrame, stubnames, i, j, sep: str = "", suffix: str = r"\d+"
) -> DataFrame:
r"""
Unpivot a DataFrame from wide to long format.
Less flexible but more user-friendly than melt.
With stubnames ['A', 'B'], this function expects to find one or more
group of columns with format
A-suffix1, A-suffix2,..., B-suffix1, B-suffix2,...
You specify what you want to call this suffix in the resulting long format
with `j` (for example `j='year'`)
Each row of these wide variables are assumed to be uniquely identified by
`i` (can be a single column name or a list of column names)
All remaining variables in the data frame are left intact.
Parameters
----------
df : DataFrame
The wide-format DataFrame.
stubnames : str or list-like
The stub name(s). The wide format variables are assumed to
start with the stub names.
i : str or list-like
Column(s) to use as id variable(s).
j : str
The name of the sub-observation variable. What you wish to name your
suffix in the long format.
sep : str, default ""
A character indicating the separation of the variable names
in the wide format, to be stripped from the names in the long format.
For example, if your column names are A-suffix1, A-suffix2, you
can strip the hyphen by specifying `sep='-'`.
suffix : str, default '\\d+'
A regular expression capturing the wanted suffixes. '\\d+' captures
numeric suffixes. Suffixes with no numbers could be specified with the
negated character class '\\D+'. You can also further disambiguate
suffixes, for example, if your wide variables are of the form A-one,
B-two,.., and you have an unrelated column A-rating, you can ignore the
last one by specifying `suffix='(!?one|two)'`. When all suffixes are
numeric, they are cast to int64/float64.
Returns
-------
DataFrame
A DataFrame that contains each stub name as a variable, with new index
(i, j).
See Also
--------
melt : Unpivot a DataFrame from wide to long format, optionally leaving
identifiers set.
pivot : Create a spreadsheet-style pivot table as a DataFrame.
DataFrame.pivot : Pivot without aggregation that can handle
non-numeric data.
DataFrame.pivot_table : Generalization of pivot that can handle
duplicate values for one index/column pair.
DataFrame.unstack : Pivot based on the index values instead of a
column.
Notes
-----
All extra variables are left untouched. This simply uses
`pandas.melt` under the hood, but is hard-coded to "do the right thing"
in a typical case.
Examples
--------
>>> np.random.seed(123)
>>> df = pd.DataFrame({"A1970" : {0 : "a", 1 : "b", 2 : "c"},
... "A1980" : {0 : "d", 1 : "e", 2 : "f"},
... "B1970" : {0 : 2.5, 1 : 1.2, 2 : .7},
... "B1980" : {0 : 3.2, 1 : 1.3, 2 : .1},
... "X" : dict(zip(range(3), np.random.randn(3)))
... })
>>> df["id"] = df.index
>>> df
A1970 A1980 B1970 B1980 X id
0 a d 2.5 3.2 -1.085631 0
1 b e 1.2 1.3 0.997345 1
2 c f 0.7 0.1 0.282978 2
>>> pd.wide_to_long(df, ["A", "B"], i="id", j="year")
... # doctest: +NORMALIZE_WHITESPACE
X A B
id year
0 1970 -1.085631 a 2.5
1 1970 0.997345 b 1.2
2 1970 0.282978 c 0.7
0 1980 -1.085631 d 3.2
1 1980 0.997345 e 1.3
2 1980 0.282978 f 0.1
With multiple id columns
>>> df = pd.DataFrame({
... 'famid': [1, 1, 1, 2, 2, 2, 3, 3, 3],
... 'birth': [1, 2, 3, 1, 2, 3, 1, 2, 3],
... 'ht1': [2.8, 2.9, 2.2, 2, 1.8, 1.9, 2.2, 2.3, 2.1],
... 'ht2': [3.4, 3.8, 2.9, 3.2, 2.8, 2.4, 3.3, 3.4, 2.9]
... })
>>> df
famid birth ht1 ht2
0 1 1 2.8 3.4
1 1 2 2.9 3.8
2 1 3 2.2 2.9
3 2 1 2.0 3.2
4 2 2 1.8 2.8
5 2 3 1.9 2.4
6 3 1 2.2 3.3
7 3 2 2.3 3.4
8 3 3 2.1 2.9
>>> l = pd.wide_to_long(df, stubnames='ht', i=['famid', 'birth'], j='age')
>>> l
... # doctest: +NORMALIZE_WHITESPACE
ht
famid birth age
1 1 1 2.8
2 3.4
2 1 2.9
2 3.8
3 1 2.2
2 2.9
2 1 1 2.0
2 3.2
2 1 1.8
2 2.8
3 1 1.9
2 2.4
3 1 1 2.2
2 3.3
2 1 2.3
2 3.4
3 1 2.1
2 2.9
Going from long back to wide just takes some creative use of `unstack`
>>> w = l.unstack()
>>> w.columns = w.columns.map('{0[0]}{0[1]}'.format)
>>> w.reset_index()
famid birth ht1 ht2
0 1 1 2.8 3.4
1 1 2 2.9 3.8
2 1 3 2.2 2.9
3 2 1 2.0 3.2
4 2 2 1.8 2.8
5 2 3 1.9 2.4
6 3 1 2.2 3.3
7 3 2 2.3 3.4
8 3 3 2.1 2.9
Less wieldy column names are also handled
>>> np.random.seed(0)
>>> df = pd.DataFrame({'A(weekly)-2010': np.random.rand(3),
... 'A(weekly)-2011': np.random.rand(3),
... 'B(weekly)-2010': np.random.rand(3),
... 'B(weekly)-2011': np.random.rand(3),
... 'X' : np.random.randint(3, size=3)})
>>> df['id'] = df.index
>>> df # doctest: +NORMALIZE_WHITESPACE, +ELLIPSIS
A(weekly)-2010 A(weekly)-2011 B(weekly)-2010 B(weekly)-2011 X id
0 0.548814 0.544883 0.437587 0.383442 0 0
1 0.715189 0.423655 0.891773 0.791725 1 1
2 0.602763 0.645894 0.963663 0.528895 1 2
>>> pd.wide_to_long(df, ['A(weekly)', 'B(weekly)'], i='id',
... j='year', sep='-')
... # doctest: +NORMALIZE_WHITESPACE
X A(weekly) B(weekly)
id year
0 2010 0 0.548814 0.437587
1 2010 1 0.715189 0.891773
2 2010 1 0.602763 0.963663
0 2011 0 0.544883 0.383442
1 2011 1 0.423655 0.791725
2 2011 1 0.645894 0.528895
If we have many columns, we could also use a regex to find our
stubnames and pass that list on to wide_to_long
>>> stubnames = sorted(
... set([match[0] for match in df.columns.str.findall(
... r'[A-B]\(.*\)').values if match != []])
... )
>>> list(stubnames)
['A(weekly)', 'B(weekly)']
All of the above examples have integers as suffixes. It is possible to
have non-integers as suffixes.
>>> df = pd.DataFrame({
... 'famid': [1, 1, 1, 2, 2, 2, 3, 3, 3],
... 'birth': [1, 2, 3, 1, 2, 3, 1, 2, 3],
... 'ht_one': [2.8, 2.9, 2.2, 2, 1.8, 1.9, 2.2, 2.3, 2.1],
... 'ht_two': [3.4, 3.8, 2.9, 3.2, 2.8, 2.4, 3.3, 3.4, 2.9]
... })
>>> df
famid birth ht_one ht_two
0 1 1 2.8 3.4
1 1 2 2.9 3.8
2 1 3 2.2 2.9
3 2 1 2.0 3.2
4 2 2 1.8 2.8
5 2 3 1.9 2.4
6 3 1 2.2 3.3
7 3 2 2.3 3.4
8 3 3 2.1 2.9
>>> l = pd.wide_to_long(df, stubnames='ht', i=['famid', 'birth'], j='age',
... sep='_', suffix=r'\w+')
>>> l
... # doctest: +NORMALIZE_WHITESPACE
ht
famid birth age
1 1 one 2.8
two 3.4
2 one 2.9
two 3.8
3 one 2.2
two 2.9
2 1 one 2.0
two 3.2
2 one 1.8
two 2.8
3 one 1.9
two 2.4
3 1 one 2.2
two 3.3
2 one 2.3
two 3.4
3 one 2.1
two 2.9
"""
def get_var_names(df, stub: str, sep: str, suffix: str) -> list[str]:
regex = rf"^{re.escape(stub)}{re.escape(sep)}{suffix}$"
pattern = re.compile(regex)
return [col for col in df.columns if pattern.match(col)]
def melt_stub(df, stub: str, i, j, value_vars, sep: str):
newdf = melt(
df,
id_vars=i,
value_vars=value_vars,
value_name=stub.rstrip(sep),
var_name=j,
)
newdf[j] = Categorical(newdf[j])
newdf[j] = newdf[j].str.replace(re.escape(stub + sep), "", regex=True)
# GH17627 Cast numerics suffixes to int/float
newdf[j] = to_numeric(newdf[j], errors="ignore")
return newdf.set_index(i + [j])
if not is_list_like(stubnames):
stubnames = [stubnames]
else:
stubnames = list(stubnames)
if any(col in stubnames for col in df.columns):
raise ValueError("stubname can't be identical to a column name")
if not is_list_like(i):
i = [i]
else:
i = list(i)
if df[i].duplicated().any():
raise ValueError("the id variables need to uniquely identify each row")
value_vars = [get_var_names(df, stub, sep, suffix) for stub in stubnames]
value_vars_flattened = [e for sublist in value_vars for e in sublist]
id_vars = list(set(df.columns.tolist()).difference(value_vars_flattened))
_melted = [melt_stub(df, s, i, j, v, sep) for s, v in zip(stubnames, value_vars)]
melted = _melted[0].join(_melted[1:], how="outer")
if len(i) == 1:
new = df[id_vars].set_index(i).join(melted)
return new
new = df[id_vars].merge(melted.reset_index(), on=i).set_index(i + [j])
return new